Copper-cobalt infiltrant for iron powder



United States Patent of New Jersey No Drawing. Filed Dec. 27, 1960, Ser.No. 78,211 3 Claims. (Cl. 75-153) This invention relates to powdermetallurgy and, more particularly, to a novel infiltrant for iron powdercompacts.

It is a well established practice to increase the strength of ironpowder compacts by infiltrating the iron compact with another metalhaving a melting point lower than that of iron. This is generally doneby placing an amount of'the infiltrant metal on the surface of thesintered iron compact sufiicient to fill the voids between the ironparticles and by then bringing the compact up to a temperaturesufficient to cause the infiltrant metal to become molten and infiltratethe iron compact. In some instances the infiltrant metal is applied to agreen compact and then the resulting product is heated to a temperaturesufficient to sinter the iron and in the meantime to cause theinfiltrant to melt and impregnate the compact. Although the resultinginfiltrated compact has a final strength greater than that of thenon-infiltrated sintered compact, there is a frequent drawback to theinfiltrated compact in that it needs machining or similar treatment toremove either a residue left from the infiltrant or a pitted surfaceproduced by the erosive action of the molten infiltrant on the surfaceof the iron compact. These difiiculties are particularly displayed bycopper and copper-base alloys which are favored infiltrants because ofthe high strength and ductility which they impart to iron powdercompacts and because of their favorable wetting action for the iron andtheir suitbale melting points.

I have now found that the inclusion in cooper of a certain amount ofcobalt imparts to the copper the ability to infiltrate an iron powdercompact without leaving any residue on the surface of the compact andwithout pitting its surface. Thus, the novel infiltrant of the presentinvention consists essentially of copper containing between 1% and 4.5%by weight of cobalt.

The infiltrant may be applied to the iron compact either in the form ofa green compact of the copper-cobalt alloy powder or in the form of asolid mass of the coppercobalt alloy. In each of these forms the properamount of infiltrant for each iron powder compact can be readilydetermined and can be controlled by the shape and size of the mass ofinfiltrant pursuant to conventional infiltration technique.

The following examples of infiltrants both within and without the scopeof the present invention will serve to demonstrate the merits of theinfiltrants of the invention. In each instance, the infiltrant was usedwith an iron powder compact obtained by compacting iron powder,containing 0.75% by weight of zinc stearate as a lubricant, at apressure of 20 t.s.i. into the form of standard tension bars of theMetal Powder Industries Federation. These bars were sintered in hydrogenfor one hour at 1120 C. The resulting iron compacts had a representativetensile strength of 17,500 psi. with an elongation of 1 to 2% atfracture. The sintered bars had a pore volume of about 26% of the barvolume.

In testing the effectiveness of each infiltrant, an amount 3,128,177Patented Apr. 7, 1964 "ice of the infiltrant was used whichapproximately 83% of the pore volume of the iron powder test barpursuant to present commercial practice. In each instance the infiltrantwas used in the form of a metal strip which was placed on the uppersurface of the sintered iron powder test bar and the assembly was heatedfor 30 minutes at 1100 C. in a hydrogen atmosphere. The resultinginfiltrated test bar was then cooled to room temperature at the rate of37 C. per minute.

The following table summarizes the test data on the aforementioned ironpowder test bars infiltrated as described with the specified infiltrant:

It will be observed from the foregoing data that pitting of or a residueon the surface of the iron powder test bar resulted from the use ofconventional infiltrants (brass or copper) and from copper-cobalt alloysoutside of the aforementioned eifective range of 1% to 4.5 by weight ofcobalt. Within this cobalt range, the cuprous infiltrants impart hightensile strength and ductility to the iron powder compact withoutadversely affecting the surface of the compact by either pitting or aresidue.

I claim:

1. An infiltrant for iron powder compacts having a melting point lowerthan that of iron and capable, when melted in contact with an ironpowder compact, of infiltrating the compact without pitting the surfaceof the compact and without leaving a residue on the surface of thecompact, said infiltrant comprising a copper-cobalt alloy consistingessentially of 1% to 4.5 by weight of cobalt and the balance copper.

2. An infiltrant for iron powder compacts having a melting point lowerthan that of iron and capable, when melted in contact with an ironpowder compact, of infiltrating the compact without pitting the surfaceof the compact and without leaving a residue on the surface of thecompact, said infiltrant comprising a copper-cobalt alloy powder theparticles of which consist essentially of 1% to 4.5% by weight of cobaltand the balance copper.

3. An infiltrant for iron powder compacts having a melting point lowerthan that of iron and capable, when melted in contact with an ironpowder compact, of infiltrating the compact without pitting the surfaceof the compact and without leaving a residue on the surface of thecompact, said infiltrant comprising a solid mass of a copper-cobaltalloy consisting essentially of 1% to 4.5% by weight of cobalt and thebalance copper.

References Cited in the file of this patent UNITED STATES PATENTS Evanset al. Jan. 6, 1959 OTHER REFERENCES

1. AN INFILTRANT FOR IRON POWDER COMPACTS HAVING A MELTING POINT LOWERTHAN THAT OF IRON AND CAPABLE, WHEN MELTED IN CONTACT WITH AN IRONPOWDER COMPACT, OF INFILTRATING THE COMPACT WITHOUT PITTING THE SURFACEOF THE COMPACT AND WITHOUT LEAVING A RESIDUE ON THE SURFACE OF THECOMPACT, SAID INFILTRANT COMPRISING A COPPER-COBALT ALLOY CONSISTINGESSENTIALLY OF 1% TO 4.5% BY WEIGHT OF COBALT AND THE BALANCE COPPER.